To make a polarizing sheet, generally a polarizing film that is obtained by absorbing or impregnating iodine or dichroic dyes into a monoaxially stretched polyvinyl alcohol (PVA) film is used. Generally, transparent resins, such as triacetylcellulose, are used on one or both sides of the polarizing film as a protective layer to make a polarizing plate. Such a polarizing plate is easily handled and is useful for secondary processing. Further, it is cheap and light.
According to the properties of resins used in protective layers, when the resin is a polycarbonate, since it has superior impact resistance, as well as high heat resistance, a polarizing sheet made from the polycarbonate is used to produce lenses for the sunglasses or the goggles obtained by a curving process and an injection-molding process.
However, since, for example, the aromatic polycarbonate has a large photoelastic constant, if the aromatic polycarbonate is curved to make a spherical or aspherical surface, such as in sunglasses or goggles, interference fringes in coloration easily arise by the retardation of the polycarbonate, and as a result, the interference fringes cause problems such as deterioration in the appearance of the article and eyestrain.
Further, in a polarizing lens obtained by curving a polarizing sheet to make a spherical or an aspherical surface, because of unevenness of the thickness of the aromatic polycarbonate polarizing sheet, distortion of images occurs. Therefore, the polarizing lens has problems in terms of causing deterioration in the appearance of the article and eyestrain.
For retardation that arises during the curving processes, the aromatic polycarbonate sheet that is used as a protective layer subjected to pre-extruding to make an aromatic polycarbonate sheet with invisible interference fringes in coloration as a result of the large retardation (hereafter referred to as a “stretched polycarbonate polarizing sheet”) was known (Reference 1). Among various polarizing sheets, this sheet is used for articles that require an excellent appearance or that need to be very eye-friendly.
Further, to produce lenses that have higher impact resistance than that of the polarizing lens obtained by curving the stretched polycarbonate lens or to produce lenses for correction that have focus refractivity, a polarizing lens that is obtained by curving the stretched polycarbonate polarizing sheet to form a spherical or aspherical surface, inserting the curved polarizing sheet into a mold, and injecting an aromatic polycarbonate into the mold to produce the lens (hereafter, “aromatic polycarbonate polarizing lens”) is known (References 2 and 3).
The aromatic polycarbonate polarizing lens is made by injecting an aromatic polycarbonate into a mold to fill the aromatic polycarbonate [in the concave surface of the curved aromatic polycarbonate sheet]. This brings about a benefit wherein the unevenness of the thickness of the stretched polycarbonate sheet that is inserted in the mold disappears. Thus, even for lenses without focus refractivity, the aromatic polycarbonate polarizing lens is used in products that require particularly excellent impact resistance or appearance or that need to be very eye-friendly.
In lenses such as aromatic polycarbonate polarizing lenses, which are obtained by inserting thermosetting resins or thermoplastic resins into molds, the shape and thickness of the molded lenses can be freely set by setting the shape of the surface of both sides of the mold and the distance between the two sides accordingly. Thus, based on the optical design, the shape and the distance between the two sides of the mold can be set so as to have the desired values of focus refractivity, prism-diopter, and image distortion.
The surface shape of the molded lens and the surface shape of the mold at the time of contact with the molded lens are generally identical. However, if a very high level of precision of the surface shape of the lens is required, to compensate for a reduction in the thickness of the lens or a change in the surface shape, which are caused by shrinking of the volume when thermosetting resins or thermoplastic resins that are injected into molds solidify, the surface shape and the distance between the two sides of the mold should be adjusted accordingly.
The surface of the aromatic polycarbonate polarizing lens that is produced in this way is subjected to further appropriate steps, such as forming a hard coat layer or an anti-reflection film, etc., and then polishing the rims of the lens, drilling, screw fastening, etc., to fix the lens to the frame, thereby making sunglasses and goggles.
In the polarizing lens obtained by applying curving processes to the aromatic polycarbonate polarizing sheet to form a spherical or an aspherical surface or the injecting polarizing lens obtained by injecting aromatic polycarbonate, for the purpose of reducing the glare of the surface of glass, the surface of water, etc., polarized light in the horizontal direction is cut. In addition, for the purpose of improving visibility or design, for example, an aromatic polycarbonate polarizing sheet colored in grey, brown, or the like, is used to provide a desired color tone and transmittance.
In order to increase the degree of polarization of a polarizing lens, the amount of dichroic dye for dyeing a polyvinyl alcohol film is adjusted to a concentration at which the polarization component in the horizontal direction of light incident on the polarizing lens is almost absorbed. And when the amount of the dichroic dye for dyeing the polyvinyl alcohol film is further increased, the polarization component in the perpendicular direction of light incident on the polarizing lens is also absorbed in a large amount. For a higher performing polarizing lens, a polarizing lens that shows decreased absorbance of the polarization component in the perpendicular direction of light incident in the polarizing lens, by using a dichroic dye that shows a higher dichroic ratio, is required.
Further, regarding the dichroic dyes for dyeing the polyvinyl alcohol film, not a single color, but several colors of dichroic dyes are used. In this regard, by changing the amount of each dichroic dye for dyeing the polyvinyl alcohol film, a polarizing lens having a desired color tone and transmittance can be obtained.
Further, a method to obtain a polarizing lens that has a desired color tone or a desired transmittance by dissolving the dyes in an adhesive layer or an aromatic polycarbonate sheet can be used. The method can control the color tone or the transmittance of an injecting polarizing sheet by itself or in combination with the steps explained above.
In a liquid crystalline material for a projection television that uses a polarizing film and color filters, a method for producing a color filter that has a polarizing function and specific absorption function of wavelengths using dichroic dyes and dyes that have low dichroic ratios was known. (Reference 4)